The present invention relates to a system for regulating the idle speed of an internal combustion engine with an electronic fuel injection system, and more particularly to a system for adjusting the volume of intake air passing through a bypass around a throttle valve so as to keep the idle speed to a predetermined speed.
Generally, the volume of intake air is measured by an air flow meter provided in an intake passage to convert to an electric air flow signal which is fed to an electronic control unit. The electronic control unit is provided with a feedback control circuit responsive to the air flow signal for producing a control signal. The control signal is applied to a solenoid for a regulator valve provided in the bypass to regulate the idle speed.
In a conventional feedback control circuit includes an engine speed sensor, an integrator for comparing the engine speed sensed by the engine speed sensor with a reference value and for producing an output, and a driver responsive to the output of the integrator to energize the solenoid of the regulator valve so as to regulate the idle speed to a predetermined speed.
On the other hand, the idle speed in one revolution of the crankshaft of the engine fluctuates by influences of operations such as compression, expansion and others. If such a fluctuation of idle speed is sensed by the engine speed sensor and idle speed is regulated, the engine speed is vainly regulated in accordance with the fluctuation and hunting of the system will occur.